This invention relates to sewing machines. More particularly, the invention relates to a mechanism for providing a needle thread loop passage between a throat plate and a shuttle-bobbin assembly.
Various types of openers for horizontal rotary shuttles have been heretofore proposed. FIGS. 1 and 2 show a shuttle-bobbin assembly where one type of conventional opener has been incorporated. The structure includes an inner shuttle guide arm 6 having a shank 6a at one end thereof and a fulcrum shaft 5 at the other end thereof. An inner shuttle guide 7 is rigidly mounted on the shank 6a at its top, a swing lever 10 is pivotally mounted on the inner shuttle guide arm 6 at the other end thereof, and an eccentric cam 9 is eccentrically rotatable about a shuttle shaft 8.
In such a conventional opener, an inner shuttle 2 containing a bobbin thread is likely to tend to be rotated when a shuttle 1 is rotated clockwise. The inner shuttle 2 is, however, prevented from rotation by having two machine frame support segments 3, 4 which are separated by a slot, the machine frame support segments downwardly extending from a throat plate 19 abutted against a projection 2a at the opposite sides thereof formed on the inner shuttle 2. In this connection, it is noted that in order to seize the needle thread loop formed by the needle with a point 1a of the shuttle 1 to pass through the shuttle for formation of stitches, the needle thread loop is required to pass between the projection 2a and the support segments 3, 4. The projection 2a, however, abuts against the support segment 3 disposed forwardly of the projection because the inner shuttle 2 is susceptible to clockwise rotation. Thus, when the inner shuttle 2 is clockwise rotated, the needle thread loop is prevented from passing between the projection 2a and the support segments 3, 4 unless a gap or clearance is formed therebetween.
An opener is provided for defining the gap or clearance between the projection and the support segments. The opener illustrated in FIGS. 1 and 2 has been well known to the sewing machine art. It has been found that the needle thread loop passes between the projection 2a and the support segments 3, 4 to rotate the eccentric cam 9, thereby dislocating the swing lever 10. This rotates the inner shuttle guide arm 6 counterclockwise about the support shaft 5 as seen in FIG. 1. As a result, the inner shuttle guide 7 is driven by the counterclockwise rotation of the inner shuttle guide arm 6 to act on a collar 11 formed on the inner shuttle 2 or a collar serving as a cap of the inner shuttle, if provided, thus slightly rotating the inner shuttle 2 counterclockwise (FIG. 1) to obtain a gap or clearance between the projection 2a and the support segment 3.
As a result point 1a tends to become worn out and is reduced to a point 1a' whenever it is contacted with a needle 12 as is best shown in FIG. 5.
A conventional horizontal rotary shuttle opener as described herein has difficulty in adjusting the stroke of the inner shuttle guide 7 to correspond to the worn out point 1a'. The inner shuttle guide 7 has been conventionally designed to pull the collar 11 counterclockwise to keep the projection 2a away from the support segment 3 so the needle thread loop can pass between the projection 2a and support segment 3. The needle thread loop is then caught or taken by the point and, thereafter, enters into the shuttle-bobbin assembly. The timing of separation of the projection from the support segment is the same with both a point 1a and a worn out point 1a'.
If the point is worn out, the inner shuttle guide 7 starts swinging when the point 1a' is not in the proper position which is closest to the needle 12. In other words, the point 1a' is separated from its suitable position by a distance of point 1a minus point 1a' so that the inner shuttle guide 7 may rotate at an unsuitable time for stitch setting. In other words, if the point is worn out, the inner shuttle guide should swing at a later time to function properly. The conventional horizontal rotary shuttle opener can not accomodate such a difference in timing.